One of the earliest events following acute nerve injury is the active process of axonal degeneration. Although axonal degeneration and debris removal are thought to be critical for successful axonal re-growth, the cellular and molecular mechanisms that underlie degeneration of injured axons are not well understood. Axonal degeneration is also a key determinant of clinical disability in hereditary neuropathies, and is highly prevalent in diabetic patients. Clearly, the lack of functional regeneration remains an important clinical problem, and is even more exuberated with age. Consequently, central to the development of novel therapeutic targets for injury and disease induced axonal degeneration is a detailed understanding of the underlying molecular triggers and cellular processes. This is in part hampered by the limited ability to monitor processes such as nerve integrity, injury and damage progression inside live mammalian animals in real time. Using laser axotomy we have established a nerve injury model in zebrafish, enabling us to visualize in real time in intact, live animals the cellular and subcellular processes during axonal degeneration, not only in injured axons but also in neighboring cell types. The objective of this proposal is to establish the zebrafish as a model organism in which to identify the molecular pathways controlling axonal degeneration, and eventually functional recovery. The experiments in this proposal will: First, determine the extent to which axonal degeneration in zebrafish is mediated by similar mechanisms as operate in higher vertebrates. Second, define pathways that impact axonal degeneration as well as regeneration. The long-term goals are to define on a cellular imaging level how injured/severed nerves reconnect with their targets, to determine the extent to which they reconstitute functional circuitries, and to identify genes and factors important for nerve regeneration. PUBLIC HEALTH RELEVANCE: Axonal degeneration is thought to be critical for successful axonal re-growth, yet the cellular and molecular mechanisms that underlie degeneration of injured axons are not well understood. Axonal degeneration and loss is also a key determinant of clinical disability in hereditary neuropathies. The objective of this proposal is to establish the zebrafish as a model organism in which to identify the molecular pathways controlling axonal degeneration, and eventually functional recovery.